1. Field of the Invention
The present invention relates to a ball joint dust cover.
Further, the present invention relates to a ball joint dust cover which is used in an automobile suspension device, and a steering device.
2. Description of the Conventional Art
Conventionally, as a ball joint to which a dust cover is installed for the purpose of preventing dust and from infiltrating in a ball joint coupling portion, there has been known a ball joint dust cover which is shown in FIG. 5 (see also, Japanese Unexamined Patent Publication No. 62-137408).
In a seal structure of this kind of ball joint dust cover, a spherical head portion 200 formed in one end of a ball stud 100 is retained within a socket 300.
Further, a shaft 400 in the other end of the ball stud 100 is fastened and fixed to a knuckle 500.
On the other hand, a large-diameter opening portion 800 formed as an approximately C-shaped cross sectional form at one end of a dust cover 600 made of a rubber-like elastic material is fixed and retained within an annular groove portion 310 which is formed in an outer peripheral surface of the socket 300 by an annular pressure ring 700, and a small-diameter opening portion 150 at the other end of the dust cover 600 is retained to the shaft 400.
The pressure ring 700 employs a circlip which is formed to have an approximately rectangular cross sectional shape.
In this kind of conventional dust cover 600, in the case that the ball stud 100 oscillates while the ball stud 100 is inclined as shown in FIG. 5, a force extending the small-diameter portion 150 is applied to the side in which a film portion of the dust cover 600 extends (a right side on the drawing). Therefore, there is generated a so-called mouth opening phenomenon of the small-diameter portion 150 in which a lip portion of the small-diameter portion 150 and the knuckle 500 are disconnected.
As a result, a seal performance in the small-diameter portion 150 is lowered, and a problem that sedimentation or garbage enters into the dust cover 600 from an external area has been brought about.
Further, it is often the case that the general dust cover has a bell shape as shown in FIG. 5, however, in the case that a diameter difference between the ball stud and the socket is reduced for the reason of downsizing of the socket, it has been deemed necessary to set the shape of the dust cover to a shape similar to a cylindrical shape in place of the bell shape.
As mentioned above, there is a tendency that the closer to the cylindrical shape of the dust cover becomes, the greater is a strain applied to the film portion of the dust cover.
As a result, a durability of the dust cover is lowered, thereby causing a problem that a part on a circumference of the film portion of the dust cover deforms to an inner diameter side at the setting time of the dust cover. Further, a problem that the small-diameter portion of the dust cover falls away from the ball stud has been brought about.
Therefore, it is desired for the shape of the dust cover to maintain the bell shape even if the diameter difference between the ball stud and the socket is reduced.